The present invention relates to an integrated circuit whereby the signal receiving circuits and display drive circuits of a miniature television receiver can be configured into a single unit which includes an integral liquid crystal display panel.
Ultra-miniature television (abbreviated hereinafter to TV) receivers employing a liquid crystal display are becoming increasingly compact, and the market demand for such receivers is expanding rapidly. A liquid crystal display TV receiver of this type includes an antenna and a tuner unit which is operable to select TV signal channels from signals picked up by the antenna, the tuner unit basically consisting of a local oscillator circuit and a mixer for performing frequency conversion of the antenna signal to an intermediate frequency (I.F.) signal. The receiver further includes an I.F. amplifier circuit for amplifying this signal, a video signal circuit for detecting and amplifying a video signal component of the amplified I.F. signal, and an audio signal circuit for detecting and amplifying an audio signal component of the I.F. signal. All of these circuits are of analog type. The receiver also includes a liquid crystal display panel and a liquid crystal display drive circuit for generating digital signals to drive the liquid crystal display panel to display video data contained in the video signal component. The liquid crystal display panel can be of passive type, i.e. consisting only of a matrix array of liquid crystal display elements, or can be of active type, i.e. in which each of the liquid crystal display elements is coupled to an individual control element such as a thin-film transistor functioning as a switch. It is possible for the techniques employed to manufacture such a miniature liquid crystal display TV receiver to be modified for manufacturing miniature display terminals, for computers or other data-processing apparatus. Thus, the field of future applications for such devices is extremely wide.
With prior art types of miniature liquid crystal display TV receivers, the analog receiving circuit section is formed of discrete components mounted on a printed circuit board or upon a ceramic substrate, and is enclosed within a metal case. These discrete components generally include an electronic tuner unit (i.e. in which channel selection is executed by variation of a bias voltage), an I.F. signal integrated circuit for I.F. amplification, an audio signal integrated circuit, a video signal integrated circuit, and various types of filters, transistors, diodes, capacitors, coils, etc., which are individually mounted as separate components upon a printed circuit board or ceramic substrate. Similarly the liquid crystal display drive circuit is generally configured as an integrated circuit, together with associated transistors, diodes, capacitors, etc., all of which are individually mounted on a printed circuit board. This circuit produces drive signals for a liquid crystal display panel.
There is an increasing trend towards making such liquid crystal display TV receivers increasingly thin and compact. However if it is attempted to achieve this by further miniaturizing the individual components of the receiver, the result will be deterioration of the electrical performance of the components, together with increased manufacturing cost. Furthermore if the components are mounted on the printed circuit board with an excessively high degree of component density, in order to achieve greater compactness, then this will lead to problems with regard to automatic component mounting during manufacture, and problems with respect to adjustment of the receiver after mounting has been completed. In addition, such increased component density will result in a higher density of formation of connecting leads which are patterned upon the printed circuit board or ceramic substrate, i.e. the connecting leads must be made of decreased width or with decreased inter-lead spacing. This leads to problems resulting from factors such as electrostatic and electromagnetic coupling, and also lowers the performance and reliability of the printed circuit board. For these reasons, it is not practicable to achieve any substantial advances towards greater compactness of miniature liquid crystal display TV receivers by modification of the conventional configuration.
The present invention relates to an integrated circuit for implementing the signal receiving and display drive functions of a TV receiver, having a plurality of layers of active circuit elements such as transistors etc., with specific elements in different layers being mutually interconnected by means of through-hole connections formed between, and in some cases passing through, various layers. With such an integrated circuit, which will be referred to hereinafter as a 3-dimensional integrated circuit, the wiring interconnections between circuit elements are implemented in three dimensions, rather than two dimensions as in the case of a conventional type of integrated circuit. Such an integrated circuit includes a plurality of vertically supermimposed layers of semiconductor material (each having active circuit elements such as transistors and generally also having passive circuit elements such as resistors etc. formed therein, together with connecting leads) which are mutually separated by layers of electrically insulating material, and has a number of advantages over a conventional two-dimensional integrated circuit. These can be summarized as follows:
(1) A high level of component density becomes practicable, with a greater degree of integration. PA0 (2) Increased operating speed is made possible. PA0 (3) Parallel processing of data is facilitated PA0 (4) A multiplicity of functions can be readily implemented.
Advantage (1) above is a direct result of the multi-layer configuration of the integrated circuit. For example if there are 10 semiconductor material layers in which are formed active circuit elements such as transistors (each of such layers being referred to hereinafter as an active semiconductor layer), then the level of integration can be considered to be ten times greater than that of a 2-dimensional integrated circuit. Furthermore it is generally unnecessary to provide individual input and output circuits (which have relatively high power consumption) in each of the circuit layers. As a result, the level of power consumption of a 3-dimensional integrated circuit can be made substantially lower than that of a 2-dimensional integrated circuit.
Advantage (2) above results from the fact that signal transmission delays, determined by connecting lead lengths, can be significantly reduced. In the case of a 2-dimensional integrated circuit the lengths of connecting leads will generally increase in proportion to the size of the integrated circuit, with corresponding increases in lead resistance. However with a 3-dimensional integrated circuit, through-hole connecting leads can be provided between the various layers, i.e. connecting leads which pass through the insulating layers between the active semiconductor layers. With a 2-dimensional integrated circuit, the connecting lead lengths may be as long as several millimeters. However in the case of a 3-dimensional integrated circuit, the maximum connecting lead length (between the uppermost and lowermost semiconductor layers) can be held to several micronmeters. Furthermore in the case of a 3-dimensional integrated circuit, circuit elements are formed upon an insulating film, and as a result the amount of self-capacitance of each component is smaller than in the case of a 2-dimensional integrated circuit. This leads to inherently higher operating speed capabilities for the circuit components.
With regard to advantage (3) above, it will be apparent that a 3-dimensional integrated circuit enables parallel data processing to be readily implemented. It is possible to provide several thousand or even several tens of thousands of through-hole connecting leads, for simultaneously transferring data between upper and lower layers of a 3-dimensional integrated circuit.
In the case of advantage (4) above, it is possible to arrange that each of the active semiconductor layers performs an independent function, or to arrange that specific groups of layers respectively function as units for executing specific functions.
However various problems arise if the use of a prior art type of 3-dimensional integrated circuit is envisaged for implementing all of the functions of a miniature liquid crystal display TV receiver within a single unit. One of these problems is that of providing the tuner section of the receiver. Since the tuner section must process signal frequencies which are extremely high (i.e. in the UHF and VHF bands), the circuit elements such as transistors and diodes etc. of that section must be capable of satisfactory operation at very high frequencies. It is advantageous to employ polycrystalline silicon layer to form the active semiconductor layers of a 3-dimensional integrated circuit, since this material can be easily deposited at a relatively low processing temperature. This reduces the danger of damage to circuit elements within underlying layers, as a result of heat transmission down through the layers, and also the danger of structural damage due to non-uniform heating of the substrate (since there will inevitably be localized differences in thickness within each of the semiconductor layers). However due to the low level of electron mobility within polycrystalline silicon, the material is not suitable for forming circuit elements which are to operate at high frequencies, such as active elements of a TV tuner unit or an I.F. amplifier. One method of forming a semiconductor layer in which active elements such as transistors can be formed which will be capable of high-frequency operation, in a 3-dimensional integrated circuit, is to initially form a layer of polycrystalline silicon layer, and to then irradiate that layer with an electron beam or laser beam for thereby heating the layer to a sufficiently high temperature (i.e. 1400.degree. C.) to melt the silicon. Recrystallization then occurs, to produce an epitaxial layer of silicon, which is employed as an active semiconductor layer. This irradiation is performed for only a very brief time, e.g. several milliseconds, so that the amount of heat which is transmitted to underlying layers of the integrated circuit can be made negligible, and no adverse effects need result. The epitaxial layer thus formed can then be appropriately doped in specific regions, to configure active elements such as transistors etc.
However with the technology which is utilized at present for such recrystallization processing of polycrystalline silicon, no layer of seed crystal is provided below that silicon layer, for controlling the direction of the preferred crystal axis (the 110 axis) of the epitaxial layer which is formed. Due to this, the direction of orientation of this crystal axis in the epitaxial layer which is formed by recrystallization processing will not be uniform throughout that layer, i.e. localized variations in the axis direction will occur throughout the layer. These difference result from the fact that the direction of the crystal axis in a region of the epitaxial layer is affected by the direction of that axis within the corresponding portion of the polycrystalline layer from which the epitaxial layer was formed. This leads to localized differences in electron mobility within that layer of the wafer in which the integrated circuits are formed. These variations in electron mobility are especially liable to occur in the upper layers of a multi-layer integrated circuit, and in addition the overall level of electron mobility within such an epitaxial layer may vary between different integrated circuits. Furthermore, the various active semiconductor layers of a 3-dimensional integrated circuit are mutually separated by layers of an insulating material which is non-crystalline, (generally silicon dioxide). The surface of such a layer of insulating material will not be precisely flat, and the amount of departure from flatness will increase as the number of circuit layers is increased. This further tends to produce non-uniformity of the crystal axis orientation, i.e. formation of a recrystallized epitaxial silicon layer upon a surface which is not perfectly flat will lead to greater degrees of localized variations in electron mobility within the layer, causing substantial non-uniformity of device characteristics of circuit elements such as transistors which are subsequently formed in that layer, and unsatisfactory performance of these elements at very high frequencis of operation. For this reason, it is difficult to form circuit elements which must function at very high frequencies, e.g. elements of a TV tuner section, by using such a recrystallized epitaxial silicon layer in a 3-dimensional integrated circuit.
Another difficulty which arises with respect to employing a 3-dimensional integrated circuit to form a unit liquid crystal display TV receiver is that the drive circuit of the liquid crystal display panel produces drive pulses which are of substantial amplitude and which contain substantial high-frequency components. As a result, electromagnetic radiation is generated by this drive circuit, which can leak into the high-gain input stages of the tuner (i.e. from the antenna) or the I.F. amplifier circuit. The resultant interference will produce severe adverse effects upon picture and sound quality of the TV receiver. Since in a 3-dimensional integrated circuit all of the semiconductor layers in which the various circuits are formed are in extremely close proximity, this is a very severe problem with respect to producing a practical liquid crystal display TV receiver as a single integrated circuit. In the case of a conventional miniature liquid crystal display TV receiver, this problem is avoided by enclosing the receiver circuits in a metallic case, and by providing sufficient physical separation between the liquid crystal display drive circuit and the input stages of the tuner and I.F. amplifier circuits.